Late 2009 27" iMac, quad core i7, A1312, EMC No. 2374 Currently has a generic fresh install of Snow Leopard 10.6.3 (from legitimate Apple OS X disc) . . . . due to frustration at not being able to have my way with Bootable Yosemite USB stick. If I knew how, I could create a bootable DVD Yosemite installer, I've got the Installer dmg file as well as DL DVDs. I have a late 2012 iMac and have been using that as my production platform. But . . . . . . this late 2009 iMac . . . . I am completely puzzled as to why this iMac will not recognize the bootable USB stick. When I execute a cold boot with the 'C' key pressed. After a prolonged grey screen, then finally the Apple logo, it defiantly goes straight to desktop screen. When I use the Snow Leopard disc and boot to the "Recovery/Installer" environment, Disk Utility does see the USB stick, I've also re-done the stick just prior to posting here, so I do not have any reason to suspect the stick is bad. Please tell me how I am being a complete moron and show me the light.